Satellite Tracking Simultaneous-Lobing Monopulse Receiving System with Polarization Diversity Capability

A 136-MHz to 10-GHz simultaneous-lobing monopulse receiving system, utilizing polarization diversity in both coherent (phase-lock) and noncoherent (nonphase-lock) operational modes, has been developed for the National Aeronautics and Space Administration (NASA) Space Tracking and Data Acquisition Network (STADAN). This sum-and-difference monopulse system, called APDAR (Advanced Polarization Diversity Autotrack Receiver), utilizes a maximalratio polarization diversity combining technique that matches the receiving antenna polarization to the incoming variable polarization from a spin-stabilized or tumbling satellite. Autotrack performance becomes independent of the incoming polarization orientation by continuous in-phase addition of the carrier-signal components from orthogonal antenna elements. This technique relies upon the principle that fading does not occur simultaneously on oppositely polarized receiving channels. APDAR results in improved autotrack performance by eliminating adverse effects of severe (over 30-dB) cross-polarization fading. The predetection diversity combining technique employed provides an average 3-dB signal-to-noise (SNR) improvement. This paper describes a series of 136-MHz satellite tracking tests and analyzes a maximal-ratio predetection diversity combiner, a three-loop phase-lock loop system, and a frequency-switched radiometer.